#include <iostream>
#include <cstring>
using namespace std;


const int N = 505;
const int INF = 0x3f3f3f3f;

int dist[N];
int g[N][N];
bool st[N];

int n, m;

// 朴素
int dijkstra(){
	for (int i = 0; i < N; i++) {
		dist[i] = INF;
	}
	dist[1] = 0;

	for (int i = 1; i <= n; i++){
		int t = -1;
		for (int j = 1; j <= n; j++) {
			if (!st[j] && (t == -1 || dist[t] > dist[j])) t = j;
		}
		st[t] = true;
		for (int j = 1; j <= n; j++) {
			dist[j] = min(dist[j], dist[t] + g[t][j]);
		}
	}

	if (dist[n] == INF){
		return -1;
	}
	return dist[n];
}

int main(){
	cin >> n >> m;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < N; j++){
			g[i][j] = INF;
		}
	}
	int a, b, c;
	while(m-- != 0){
		cin >> a >> b >> c;
		g[a][b] = min(g[a][b], c);
	}
	cout << dijkstra();
	return 0;
}
